For decades now, we’ve known that polar bears are threatened by the loss of sea ice due to climate change. But a newly discovered subpopulation of polar bears living in Southeast Greenland is giving scientists hope for how the bears might persist in the future.
Most of the polar bears we know about rely on sea ice to mate, raise cubs and hunt their prey, such as ringed seals. The calories provided by seals can help the bears store energy for months, when food and sea ice are scarcer. Climate change, however, is causing the Arctic to warm more than twice as fast as the rest of the planet and sea ice to rapidly melt and disappear. When that happens, polar bears must move on land, which affords them fewer opportunities for food.
But a small, special, genetically distinct group of polar bears in Southeast Greenland is surviving—even with limited access to sea ice—by hunting from freshwater ice supplied by Greenland’s Ice Sheet. Because this isolated population is genetically different and uniquely adapted to its environment, studying it could shed light on the future of the species in the rapidly warming Far North.
Polar bears tend to live solitary lives, except when they are mating; when many bears are attracted to a food source, such as a beached whale; or when a female raising her cubs forms a family group. ©Eric Rock
Small numbers and living alone
While scientists knew there were some polar bears, roughly a few hundred, in the Southeast Greenland area from historical records and Indigenous knowledge, they never expected to find a new subpopulation living there—and, they say, they didn’t know how special they were.
Until recently, Greenland’s remote southeast region had been poorly studied because of its heavy snowfall, jagged mountains and unpredictable weather. But now with seven years of newly collected genetic, movement and population data along the southeastern coast of Greenland—combined with 30 years of historical data from the island’s whole east coast—the researchers were able to show how these bears use glacier ice to survive with limited access to sea ice.
Publishing their results in the June 16, 2022, issue of the journal Science, the scientists say that body measurements of these bears suggest that adult females are smaller than in most regions. They also have fewer cubs, which may reflect the challenge of finding mates in their complex landscape of fjords and mountains. The genetic difference between these bears and their nearest genetic neighbors, though, is what’s astounding: greater than that observed for any of the 19 previously known polar bear populations.
Based on satellite telemetry data from 1993–2021, this map shows the Southeast Greenland polar bear habitat (purple) compared to that of the neighboring subpopulation in Northeast Greenland (orange). Polar bears in the southeast are found across 10,714 square miles of mountainous and glaciated coastal habitat; bears in the northeast are located across 259,155 square miles of mostly sea ice. ©NASA Earth Observatory
In fact, these polar bears are the most genetically isolated population of polar bears anywhere on the planet and have been living separately from other polar bear populations for at least several hundred years. The earliest known reference to bears in this location dates to the 1300s, and the first written record of the animals among the region’s fjords is from the 1830s. Their population size throughout all this time remained small.
Part of the reason these bears are so isolated, researchers believe, is because they are hemmed in on all sides: by the sharp mountain peaks and the massive Greenland Ice Sheet to the west, the open water of the Denmark Strait to the east and by the fast-flowing East Greenland coastal current that poses a hazard offshore. Thus, the bears stick close to home and have limited access to sea ice.
Indigenous knowledge and a homebody habitat
Before starting the fieldwork, the research team for this study spent two years soliciting input and gathering information from polar bear subsistence hunters in East Greenland. Hunters participated throughout the study, contributing their expertise and providing harvest samples for genetic analysis.
Although about half of a polar bear’s life is spent hunting for food, their hunts are rarely successful (less than 2 percent). A polar bear’s main prey consists of bearded and ringed seals, which they hunt in a variety of ways: waiting at breathing holes or at the water’s edge, stalking seals that have hauled out to rest on the ice or breaking into pupping dens. ©Mike Bruscia
Satellite tracking of adult females showed that, unlike most other polar bears that travel far over sea ice to hunt, Southeast Greenland bears are homebodies. They walk on ice inside protected fjords or scramble up mountains to reach neighboring fjords over the Greenland Ice Sheet. Half of the 27 tracked bears accidentally floated an average of 120 miles south on small ice floes caught in the East Greenland coastal current, but then hopped off and walked back north on land to their home fjord.
Sea ice provides the platform that most of the Arctic’s roughly 26,000 polar bears use to hunt seals. But Southeast Greenland bears have access to sea ice for only four months, between February and late May, and they can’t fast for eight months. So, for two-thirds of the year, the Southeast Greenland polar bears rely on a different strategy: they hunt seals from chunks of freshwater ice that break off the Greenland Ice Sheet and float at the front of glaciers—a mixture known as melange.
While marine-terminating glaciers, also known as tidewater glaciers (glaciers that terminate in the sea where they discharge icebergs into the ocean through the process of calving), do exist in other places in the Arctic, the unique combination of the fjord shapes, the high production of glacier ice and the very big reservoir of ice that is available from the Greenland Ice Sheet in Southeast Greenland are what currently provides a steady supply of ice for these bears. The fact that polar bears can survive here suggests that marine-terminating glaciers—and especially those regularly calving ice into the ocean—could become small-scale, climate refugia, places where some polar bears could survive as sea ice on the ocean’s surface declines. Similar habitats exist at marine-terminating glaciers on other parts of Greenland’s coast and on the island of Svalbard, a Norwegian territory located east of Greenland.
Marine-terminating glaciers, such as this one in Spitsbergen, end in the sea. Their main method of ice loss is through iceberg calving, instead of surface melt. These glaciers can either be grounded—where the glacier is in constant contact with the bed—or they can be floating, where the terminus is floating on the seawater or flowing into an ice shelf. Grounded glaciers tend to be in temperate regions, such as Alaska or Canada. Floating marine-terminating glaciers are commonly found in the polar regions, namely Antarctica, Greenland and Svalbard.
Scientists say that even with the rapid changes happening to the Greenland Ice Sheet, this area in Southeast Greenland has the potential to continue to produce glacial ice with a coast that may look like today for a long time to come.
Glacier environments and future scenarios
The authors of the Science study say that if you’re concerned about preserving polar bears, then, yes, their findings are hopeful. The sea ice conditions in Southeast Greenland today resemble what’s predicted for Northeast Greenland by late this century. Unfortunately, though, glacier habitat is not going to support huge numbers of polar bears. There’s just not enough of it. The glacier ice that makes it possible for Southeast Greenland bears to survive is not available in most of the Arctic.
Large declines in polar bear numbers across the Arctic under climate change are still expected. Longer-term monitoring will be needed to know the future viability of the Southeast Greenland bears and to understand what happens to polar bear subpopulations as they become increasingly cut off from the rest of the Arctic by declining sea ice.
While our planet does undergo long-term climate cycles, today our climate is changing faster and more dramatically due to human effects. Polar bears are remarkable animals that have evolved to excel in a remote environment—and they’re showing us that they are still capable of adapting to changing habitats. ©Eric Rock
For now, the government of Greenland will decide on any management and protection measures. The International Union for Conservation of Nature, which helps oversee protected species, is responsible for determining whether the Southeast Greenland polar bears will be internationally recognized as a separate population, the 20th in the world. Officially recognizing them as a separate population would be important for conservation and management.
For now, though, we know that the polar bears in Southeast Greenland have adapted to life in a place where sea ice is scant for much of the year.
And that’s something that we all may soon have to do.
Here’s to finding your true places and natural habitats,
Candy
